The functional vessels of human and animal bodies, such as blood vessels and ducts, occasionally weaken or even rupture. For example, an aortic wall can weaken, resulting in an aneurysm. Upon further exposure to hemodynamic forces, such an aneurysm can rupture. In Western European and Australian men who are between 60 and 75 years of age, aortic aneurysms greater than 29 mm in diameter are found in 6.9% of the population, and those greater than 40 mm are present in 1.8% of the population.
One intervention for weakened, aneurismal, dissected or ruptured vessels is the use of an endoluminal device or prosthesis such as a stent graft to provide some or all of the functionality of the original, healthy vessel and/or preserve any remaining vascular integrity by replacing a length of the existing vessel wall that contains the site of vessel weakness or failure. Stent grafts for endoluminal deployment are generally formed from a tube of a biocompatible material in combination with one or more stents to maintain a lumen therethrough. Stent grafts effectively exclude the defect by sealing both proximally and distally to the defect, and shunting blood through its length. A device of this type can, for example, treat various arterial aneurysms, including those in the thoracic aorta or abdominal aorta.
A bifurcated stent graft, one example of an endoluminal prosthesis, is known for use in treating abdominal aortic aneurysms, where the stent graft at the proximal end defines a single lumen for placement within the aorta and at the other end bifurcates into the iliac arteries. One such stent graft, disclosed in PCT application WO98/53761, is useful for repair of abdominal aortic aneurysms. That application discloses a stent graft that includes a sleeve or tube of biocompatible graft material such as woven polyester fabric or polytetrafluoroethylene (PTFE) defining a main lumen and two iliac limbs. The stent graft further includes several stents secured therealong. The stent graft is designed to span an aneurysm that extends along the aorta between the iliac and renal arteries. Unbifurcated stent grafts, in which the distal portion extends into only one iliac artery in treating an abdominal aorta, or which are used to treat the thoracic aorta are also used.
In the WO98/53761 application, the fabric-covered portion of the single-lumen proximal end of the stent graft bears against the wall of the aorta above the aneurysm and distal to the renal arteries to seal off the aneurysm. Thin wire struts of a juxtarenal attachment stent traverse the renal artery ostia without occluding them. Barbs on the attachment stent help anchor the stent graft in place.
One stent graft approved by the Food and Drug Administration (FDA) to treat aortic aneurysms is the ZENITH® AAA Endovascular Graft (Cook Incorporated, Bloomington, Ind.). The ZENITH® AAA Endovascular Graft is made up of three prosthetic modules: a bifurcated main body module and two leg modules. The main body is positioned in the aorta. The legs are positioned in the iliac arteries and connect to the main body. The stent graft thus extends from a section of the aorta, typically below the renal arteries and into both iliac arteries. The graft material is made of a woven polyester fabric like that used in open surgical repair. Standard surgical suturing techniques are used to sew the graft material to a frame of stainless steel stents. These self-expanding stents provide support for the graft material.
An endoluminal prosthesis may be comprised of multiple prosthetic modules. A modular prosthesis allows a surgeon to accommodate a wide variation in vessel morphology while reducing the necessary inventory of differently sized prostheses. For example, aortas vary in length, diameter and angulation between the renal artery region and the region of the aortic bifurcation. Prosthetic modules that fit each of these variables can be assembled to form a prosthesis, obviating the need for a custom prosthesis or large inventories of prostheses that accommodate all possible combinations of these variables. A modular system may also accommodate deployment options by allowing the proper placement of one module before the implantation of an adjoining module.
Modular prostheses are typically assembled in situ by overlapping the tubular ends of the prosthetic modules so that the end of one module sits partially inside the other module, preferably forming circumferential apposition through the overlap region. This attachment process is called “telescoping.” The connections between prosthetic modules are typically maintained by the friction forces at the overlap region and enhanced by the radial force exerted by the internal prosthetic module on the external prosthetic modules where the two overlap. The fit may be further enhanced by stents attached to the modules at the overlap region.
In many cases, however, the damaged or defected portion of the vasculature may include a branch vessel. For example, in the case of the abdominal aorta, there are at least three branch vessels, including the celiac, mesenteric, and renal arteries, leading to various other body organs. Thus, when the damaged portion of the vessel includes one or more of these branch vessels, some accommodation must be made to ensure that the stent graft does not block or hinder blood flow through the branch vessel.
Attempts to maintain blood flow to branch vessels have included providing one or more fenestrations or holes in the side wall of the stent graft. Other attempts have included providing a stent graft in which the branch vessel portion of the vessel is spanned by wires or the like. These devices have been used to treat diseased vessels, such as abdominal aortic aneurysms within the aorta that extend to or above the renal, celiac and/or mesenteric arteries. Generally, this treatment involves aligning the fenestrations with the branch vessels, which may extend approximately at right angles on both sides from the aorta.
In many cases, the vasculature is not symmetric. In addition, even with symmetrical vasculature, physiological forces may cause a previously placed branch vessel stent graft to shift causing the position of the fenestration with respect to the branch vessel to become offset. In other instances, the diseased vasculature may extend into the branch vessel and affects the ostium of the branch vessel. In some circumstances the branch vessel stent graft deployed within the main vessel may not properly seal and secure to the branch vessel and lead to leaks (endoleaks) between the branch vessel stent graft and the main vessel, a reduced blood flow to the branch vessels, and/or obscure access to portions of the branch vessel, necessitating further interventional procedures.
When treating a vessel with an endoluminal prosthesis, it may therefore be preferable to preserve the original circulation by providing a prosthetic branch that extends from the prosthesis to a side branch vessel so that the blood flow into the branch vessel is not impeded. For example, the aortic section of the ZENITH® abdominal aortic stent graft (Cook Incorporated, Bloomington, Ind.), described above, can be designed to extend above the renal arteries, and/or the celiac or mesenteric arteries, and to have prosthetic side branches that extend into the renal arteries. Branch vessel prostheses can form a connection to an aortic stent graft through fenestrations in the stent graft to complete the prosthesis. Furthermore, some aneurysms extend into the branch vessels in both the thoracic and abdominal aorta. Deploying prostheses with prosthetic branches into these vessels may help prevent expansion and/or rupture of these aneurysms.
In other situations, it may not be necessary to form a lumen that extends into the branch vessel, i.e. a stent graft. Instead, it may only be necessary to maintain patency of the branch vessel by propping the walls of the branch vessel open, also known as “stenting.” In these situations, the branch vessel prosthesis can be a mere stent, also known as an “open stent” or “bare stent.”
Thus, there remains a need for a device a branch vessel stent or stent graft to secure and seal the branch vessel stent graft to a branch vessel and within a fenestrated device.